System and method for efficient air dehumidification and liquid recovery

ABSTRACT

The present invention relates to systems and methods for dehumidifying air by establishing a humidity gradient across a water selective permeable membrane in a dehumidification unit. Water vapor from relatively humid atmospheric air entering the dehumidification unit is extracted by the dehumidification unit without substantial condensation into a low pressure water vapor chamber operating at a partial pressure of water vapor lower than the partial pressure of water vapor in the relatively humid atmospheric air. For example, water vapor is extracted through a water permeable membrane of the dehumidification unit into the low pressure water vapor chamber. As such, the air exiting the dehumidification unit is less humid than the air entering the dehumidification unit. The low pressure water vapor extracted from the air is subsequently condensed and removed from the system at ambient conditions.

BACKGROUND

Heating, ventilating, and air conditioning (HVAC) systems often havedehumidification systems integrated into the cooling apparatus fordehumidifying the air being conditioned by such systems. When cooling isrequired in warm to hot environments, the air being cooled anddehumidified will usually have a humidity ratio above approximately0.009 (pounds of H₂O per pounds of dry air). In these environments, theHVAC systems traditionally use refrigerant compressors for sensiblecooling of the air and removal of latent energy (i.e., humidity). Theair is typically cooled to about 55° F., which condenses H₂O out of theair until the air is about 100% saturated (i.e., relative humidity atabout 100%). The 55° F. temperature lowers the humidity ratio to about0.009 pounds of H₂O per pounds of dry air, which is the water vaporsaturation point at 55° F., resulting in a relative humidity of almost100%. When this air warms to about 75° F., the humidity ratio remainsapproximately the same, and the relative humidity drops to approximately50%. This traditional method of dehumidification requires the air to becooled to about 55° F., and can usually achieve a coefficient ofperformance (COP) of approximately 3-5.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the present disclosureare summarized in the following. These embodiments are not intended tolimit the scope of the claimed invention, but rather these embodimentsare intended only to provide a brief summary of possible forms of theinvention. Indeed, the invention may encompass a variety of forms thatmay be similar to or different from the embodiments set forth in thefollowing.

In a first embodiment, a dehumidification system for removing watervapor from an airstream is provided. The dehumidification systemincludes a first and second channel separated by a membrane. Themembrane is configured to facilitate removal of water vapor from anairstream flowing through the first channel by facilitating passage ofH₂O from the water vapor to the second channel through permeable volumesof the membrane while substantially blocking all other components of theairstream from passing through the membrane. The dehumidification systemalso includes a pressure increasing device configured to create a lowerpartial pressure of water vapor within the second channel than in thefirst channel, such that the H₂O moves through the membrane to thesecond channel. The pressure increasing device is also configured toincrease the pressure of water vapor at an outlet of the pressureincreasing device to a partial pressure of water vapor in a rangesuitable for subsequent condensing into liquid water. Thedehumidification system further includes a condensation deviceconfigured to receive the water vapor from the pressure increasingdevice and condense the water vapor into liquid water. In addition, thedehumidification system includes a water transport device configured totransport the liquid water from the condensation device.

In a second embodiment, a system includes a dehumidification system forremoving H₂O vapor from an airstream. The dehumidification systemincludes an air channel configured to receive an inlet airstream anddischarge an outlet airstream. The dehumidification system also includesan H₂O permeable material adjacent to the air channel. The H₂O permeablematerial is configured to selectively enable H₂O from H₂O vapor in theinlet airstream to pass through the H₂O permeable material to a suctionside of the H₂O permeable material and substantially block othercomponents in the inlet airstream from passing through the H₂O permeablematerial to the suction side of the H₂O permeable material. Thedehumidification system further includes a pressure increasing deviceconfigured to create a lower partial pressure of H₂O vapor on thesuction side of the H₂O permeable material than the partial pressure ofthe H₂O vapor in the inlet airstream to drive passage of the H₂O fromthe H₂O vapor in the inlet airstream through the H₂O permeable material,and to increase the pressure at an outlet of the pressure increasingdevice to a partial pressure of H₂O vapor suitable for condensing H₂Ovapor into liquid H₂O. In addition, the dehumidification system includesa condensation device configured to receive the H₂O vapor from theoutlet of the pressure increasing device, and to condense the H₂O vaporinto liquid H₂O.

In a third embodiment, a method includes using a pressure differentialacross an H₂O permeable material to provide a force to move H₂O throughthe H₂O permeable material into an H₂O vapor channel. The method alsoincludes receiving H₂O vapor from the H₂O permeable material into theH₂O vapor channel. The method further includes receiving the H₂O vaporfrom the H₂O vapor channel into a pressure increasing device andexpelling the H₂O vapor from the pressure increasing device at aslightly increased partial pressure of H₂O vapor. In addition, themethod includes receiving the H₂O vapor from the pressure increasingdevice into a condensation device and condensing the H₂O vapor intoliquid H₂O. The method also includes transporting the liquid H₂O fromthe condensation device to ambient conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of embodiments of thepresent disclosure will become better understood when the followingdetailed description is read with reference to the accompanying drawingsin which like characters represent like parts throughout the drawings,wherein:

FIG. 1 is a schematic diagram of an HVAC system having adehumidification unit in accordance with an embodiment of the presentdisclosure;

FIG. 2A is a perspective view of the dehumidification unit of FIG. 1having multiple parallel air channels and water vapor channels inaccordance with an embodiment of the present disclosure;

FIG. 2B is a perspective view of the dehumidification unit of FIG. 1having a single air channel located inside a single water vapor channelin accordance with an embodiment of the present disclosure;

FIG. 3 is a plan view of an air channel and adjacent water vaporchannels of the dehumidification unit of FIGS. 1, 2A, and 2B inaccordance with an embodiment of the present disclosure;

FIG. 4 is a perspective view of a separation module formed using amembrane that may be used as a water vapor channel of thedehumidification unit of FIGS. 1-3 in accordance with an embodiment ofthe present disclosure;

FIG. 5 is a psychrometric chart of the temperature and the humidityratio of the moist air flowing through the dehumidification unit ofFIGS. 1-3 in accordance with an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of the HVAC system and thedehumidification unit of FIG. 1 having a vacuum pump for removingnoncondensable components from the water vapor in the water vaporextraction chamber of the dehumidification unit in accordance with anembodiment of the present disclosure; and

FIG. 7 is a schematic diagram of the HVAC system and thedehumidification unit of FIG. 6 having a control system for controllingvarious operating conditions of the HVAC system and the dehumidificationunit in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Specific embodiments of the present disclosure will be described herein.In an effort to provide a concise description of these embodiments, allfeatures of an actual implementation may not be described in thespecification. It should be appreciated that in the development of anysuch actual implementation, as in any engineering or design project,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time-consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The subject matter disclosed herein relates to dehumidification systemsand, more specifically, to systems and methods capable of dehumidifyingair without initial condensation by establishing a humidity gradient ina dehumidification unit. In one embodiment, a water vapor permeablematerial (i.e., a water vapor permeable membrane) is used along at leastone boundary separating an air channel from a secondary channel orchamber to facilitate the removal of water vapor from the air passingthrough the air channel. The secondary channel or chamber separated fromthe air channel by the water vapor permeable material may receive watervapor extracted from the air channel via the water vapor permeablematerial.

In operation, the water vapor permeable material allows the flow of H₂O(which may refer to H₂O as water molecules, gaseous water vapor, liquidwater, adsorbed/desorbed water molecules, absorbed/desorbed watermolecules, or combinations thereof) through the water vapor permeablematerial from the air channel to the secondary channel or chamber, whilesubstantially blocking the flow of other components of the air flowingthrough the air channel from passing through the water vapor permeablematerial. As such, the water vapor permeable material reduces thehumidity of the air flowing through the air channel by removingprimarily only water vapor from the air. Correspondingly, the secondarychannel or chamber is filled with primarily water vapor. It should benoted that the passage of H₂O through the water vapor permeable materialmay be facilitated by a pressure differential. Indeed, a lower partialpressure of water vapor (i.e., a partial pressure less than the partialpressure of water vapor in the air channel) may be created in thesecondary channel or chamber to further facilitate passage of the H₂Othrough the water vapor permeable material. Accordingly, the side of thewater vapor permeable material opposite the air channel may be referredto as the suction side of the water vapor permeable material.

Once the H₂O has been passed through the water vapor permeable material,a vacuum pump is used to increase the partial pressure of the watervapor on the suction side of the water vapor permeable material to aminimal saturation pressure required to enable condensation of the watervapor by a condenser. That is, the vacuum pump compresses the watervapor to a pressure in a range suitable for condensing the water vaporinto liquid water (e.g., a range of approximately 0.25-1.1 pounds persquare inch absolute (psia), with the higher value applying toembodiments using multiple dehumidification units in series), dependingon desired conditions for condensation. The condenser then condenses thewater vapor into a liquid state, and the resulting liquid water is thenpressurized to approximately atmospheric pressure, such that the liquidwater may be rejected at ambient atmospheric conditions. By condensingthe water vapor to a liquid state prior to expelling it, certainefficiencies are provided. For example, pressurizing liquid water toatmospheric pressure requires less energy than pressurizing water vaporto atmospheric pressure. It should also be noted that thedehumidification unit described herein in general uses significantlyless energy than conventional systems.

While the embodiments described herein are primarily presented asenabling the removal of water vapor from air, other embodiments mayenable the removal of other H₂O components from air. For example, incertain embodiments, instead of a water vapor permeable material, an H₂Opermeable material may be used. As such, the H₂O permeable material mayallow the flow of one, all, or any combination of H₂O components (i.e.,water molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth)through the H₂O permeable material from the air channel to the secondarychannel or chamber, while substantially blocking the flow of othercomponents of the air flowing through the air channel from passingthrough the H₂O permeable material. In other words, the disclosedembodiments are not limited to the removal of water vapor from air, butrather to the removal of H₂O (i.e., in any of its states) from air.However, for conciseness, the embodiments described herein are primarilyfocused on the removal of water vapor from air.

FIG. 1 is a schematic diagram of an HVAC system 10 having adehumidification unit 12 in accordance with an embodiment of the presentdisclosure. As illustrated, the dehumidification unit 12 may receiveinlet air 14A having a relatively high humidity and expel outlet air 14Bhaving a relatively low humidity. In particular, the dehumidificationunit 12 may include one or more air channels 16 through which the air 14(i.e., the inlet air 14A and the outlet air 14B) flows. In addition, thedehumidification unit 12 may include one or more water vapor channels 18adjacent to the one or more air channels 16. As illustrated in FIG. 1,the air 14 does not flow through the water vapor channels 18. Rather,the embodiments described herein enable the passage of water vapor fromthe air 14 in the air channels 16 to the water vapor channels 18, thusdehumidifying the air 14 and accumulating water vapor in the water vaporchannels 18. In particular, water vapor from the air 14 in the airchannels 16 may be allowed to flow through an interface 20 (i.e., abather or membrane) between adjacent air channels 16 and water vaporchannels 18, while the other components (e.g., nitrogen, oxygen, carbondioxide, and so forth) of the air 14 are blocked from flowing throughthe interface 20. In general, the water vapor channels 18 are sealed tocreate the low pressure that pulls the water vapor from the air 14 inthe air channels 16 through the interfaces 20 as H₂O (i.e., as watermolecules, gaseous water vapor, liquid water, adsorbed/desorbed watermolecules, absorbed/desorbed water molecules, and so forth, through theinterfaces 20).

As such, a humidity gradient is established between the air channels 16and adjacent water vapor channels 18. The humidity gradient is generatedby a pressure gradient between the air channels 16 and adjacent watervapor channels 18. In particular, the partial pressure of water vapor inthe water vapor channels 18 is maintained at a level lower than thepartial pressure of water vapor in the air channels 16, such that thewater vapor in the air 14 flowing through the air channels 16 tendstoward the suction side (i.e., the water vapor channels 18 having alower partial pressure of water vapor) of the interfaces 20.

Components of air other than H₂O may be substantially blocked frompassing through the interfaces 20 in accordance with presentembodiments. In other words, in certain embodiments, approximately 95%or more, approximately 96% or more, approximately 97% or more,approximately 98% or more, or approximately 99% or more of components ofthe air 14 other than H₂O (e.g., nitrogen, oxygen, carbon dioxide, andso forth) may be blocked from passing through the interfaces 20. Whencompared to an ideal interface 20 that blocks 100% of components otherthan H₂O, an interface 20 that blocks 99.5% of components other than H₂Owill experience a reduction in efficiency of approximately 2-4%. Assuch, the components other than H₂O may be periodically purged tominimize these adverse effects on efficiency.

FIG. 2A is a perspective view of the dehumidification unit 12 of FIG. 1having multiple parallel air channels 16 and water vapor channels 18 inaccordance with an embodiment of the present disclosure. In theembodiment illustrated in FIG. 2A, the air channels 16 and the watervapor channels 18 are generally rectilinear channels, which provide asubstantial amount of surface area of the interfaces 20 between adjacentair channels 16 and water vapor channels 18. Further, the generallyrectilinear channels 16, 18 enable the water vapor 26A to be removedalong the path of the air channels 16 before the air 14 exits the airchannels 16. In other words, the relatively humid inlet air 14A (e.g.,air with a dew point of 55° F. or higher such that the air isappropriate for air conditioning) passes straight through the airchannels 16 and exits as relatively dry outlet air 14B because moisturehas been removed as the air 14 traverses along the atmospheric pressureside of the interfaces 20 (i.e., the side of the interfaces 20 in theair channels 16). In an embodiment where a single unit is dehumidifyingto a 60° F. saturation pressure or below, the suction side of theinterfaces 20 (i.e., the side of the interfaces 20 in the water vaporchannels 18) will generally be maintained at a partial pressure of watervapor that is lower than the partial pressure of water vapor on theatmospheric pressure side of the interfaces 20.

As illustrated in FIG. 2A, each of the water vapor channels 18 isconnected with a water vapor channel outlet 22 through which the watervapor in the water vapor channels 18 is removed. As illustrated in FIG.2A, in certain embodiments, the water vapor channel outlets 22 may beconnected via a water vapor outlet manifold 24, wherein the water vapor26A from all of the water vapor channels 18 is combined in a singlewater vapor vacuum volume 28, such as a tube or a chamber. Otherconfigurations of the air channels 16 and the water vapor channels 18may also be implemented. As another example, FIG. 2B is a perspectiveview of the dehumidification unit 12 of FIG. 1 having a single airchannel 16 located inside a single water vapor channel 18 in accordancewith an embodiment of the present disclosure. As illustrated, the airchannel 16 may be a cylindrical air channel located within a largerconcentric cylindrical water vapor channel 18. The embodimentsillustrated in FIGS. 2A and 2B are merely exemplary and are not intendedto be limiting.

FIG. 3 is a plan view of an air channel 16 and adjacent water vaporchannels 18 of the dehumidification unit 12 of FIGS. 1, 2A, and 2B inaccordance with an embodiment of the present disclosure. In FIG. 3, adepiction of the water vapor 26 is exaggerated for illustrationpurposes. In particular, the water vapor 26 from the air 14 is shownflowing through the interfaces 20 between the air channel 16 and theadjacent water vapor channels 18 as H₂O (i.e., as water molecules,gaseous water vapor, liquid water, adsorbed/desorbed water molecules,absorbed/desorbed water molecules, and so forth, through the interfaces20). Conversely, other components 30 (e.g., nitrogen, oxygen, carbondioxide, and so forth) of the air 14 are illustrated as being blockedfrom flowing through the interfaces 20 between the air channel 16 andthe adjacent water vapor channels 18.

In certain embodiments, the interfaces 20 may include membranes that arewater vapor permeable and allow the flow of H₂O through permeablevolumes of the membranes while blocking the flow of the other components30. Again, it should be noted that when the H₂O passes through theinterfaces 20, it may actually pass as one, all, or any combination ofstates of water (e.g., as water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth)through the interfaces 20. For example, in one embodiment, theinterfaces 20 may adsorb/desorb water molecules. In another example, theinterfaces 20 may adsorb/desorb water molecules and enable passage ofwater vapor. In other embodiments, the interfaces 20 may facilitate thepassage of water in other combinations of states. The interfaces 20extend along the flow path of the air 14. As such, the water vapor 26 iscontinuously removed from one side of the interface 20 as the relativelyhumid inlet air 14A flows through the air channel 16. Therefore,dehumidification of the air 14 flowing through the air channel 16 isaccomplished by separating the water vapor 26 from the other components30 of the air 14 incrementally as it progresses along the flow path ofthe air channel 16 and continuously contacts the interfaces 20 adjacentto the air channel 16 from the inlet air 14A location to the outlet air14B location.

In certain embodiments, the water vapor channels 18 are evacuated beforeuse of the dehumidification unit 12, such that a lower partial pressureof the water vapor 26 (i.e., a partial pressure less than the partialpressure of water vapor in the air channels 16) is created in the watervapor channels 18. For example, the partial pressure of the water vapor26 in the water vapor channels 18 may be in the range of approximately0.10-0.25 psia during normal operation, which corresponds todehumidifying to a 60° F. saturation pressure or below. In this example,an initial condition in the 0.01 psia range may be used to removenoncondensables, whereas the partial pressure of water vapor in the airchannels 16 may be in the range of approximately 0.2-1.0 psia. However,at certain times, the pressure differential between the partial pressureof the water vapor in the water vapor channels 18 and the air channels16 may be as low as (or lower than) 0.01 psia. The lower partialpressure of water vapor in the water vapor channels 18 furtherfacilitates the flow of water vapor 26 from the air channels 16 to thewater vapor channels 18 because the air 14 flowing through the airchannels 16 is at local atmospheric pressure (i.e., approximately 14.7psia at sea level). Since the partial pressure of water vapor in the air14 in the air channels 16 is greater than the partial pressure of thewater vapor 26 in the water vapor channels 18, a pressure gradient iscreated from the air channels 16 to the water vapor channels 18. Asdescribed previously, the interfaces 20 between adjacent air channels 16and water vapor channels 18 provide a barrier, and allow substantiallyonly water vapor 26 to flow from the air 14 in the air channels 16 intothe water vapor channels 18. As such, the air 14 flowing through the airchannels 16 will generally decrease in humidity from the inlet air 14Ato the outlet air 14B.

The use of water vapor permeable membranes as the interfaces 20 betweenthe air channels 16 and the water vapor channels 18 has many advantages.In particular, in some embodiments, no additional energy is required togenerate the humidity gradient from the air channels 16 to the watervapor channels 18. In addition, in some embodiments, no regeneration isinvolved and no environmental emissions (e.g., solids, liquids, orgases) are generated. Indeed, in accordance with one embodiment,separation of the water vapor 26 from the other components 30 of the air14 via water permeable membranes (i.e., the interfaces 20) can beaccomplished at energy efficiencies much greater than compressortechnology used to condense water directly from the airstream.

Because water vapor permeable membranes are highly permeable to watervapor, the costs of operating the dehumidification unit 12 may beminimized because the air 14 flowing through the air channels 16 doesnot have to be significantly pressurized to facilitate the passage ofH₂O through the interfaces 20. Water vapor permeable membranes are alsohighly selective to the permeation of the water vapor from the air 14.In other words, water vapor permeable membranes are very efficient atpreventing components 30 of the air 14 other than water vapor fromentering the water vapor channels 18. This is advantageous because theH₂O passes through the interfaces 20 due to a pressure gradient (i.e.,due to the lower partial pressures of water vapor in the water vaporchannels 18) and any permeation or leakage of air 14 into the watervapor channels 18 will increase the power consumption of the vacuum pumpused to evacuate the water vapor channels 18. In addition, water vaporpermeable membranes are rugged enough to be resistant to aircontamination, biological degradation, and mechanical erosion of the airchannels 16 and the water vapor channels 18. Water vapor permeablemembranes may also be resistant to bacteria attachment and growth inhot, humid air environments in accordance with one embodiment.

One example of a material used for the water vapor permeable membranes(i.e., the interfaces 20) is zeolite supported on thin, porous metalsheets. In particular, in certain embodiments, an ultrathin (e.g., lessthan approximately 2 μm), dense zeolite membrane film may be depositedon an approximately 50 μm thick porous metal sheet. The resultingmembrane sheets may be packaged into a membrane separation module to beused in the dehumidification unit 12. FIG. 4 is a perspective view of aseparation module 32 formed using a membrane that may be used as a watervapor channel 18 of the dehumidification unit 12 of FIGS. 1-3 inaccordance with an embodiment of the present disclosure. Two membranesheets 34, 36 may be folded and attached together into a generallyrectangular shape with a channel for the water vapor having a widthw_(msm) of approximately 5 mm The separation module 32 may be positionedwithin the dehumidification unit 12 such that the membrane coatingsurface is exposed to the air 14. The thinness of the metal supportsheet reduces the weight and cost of the raw metal material and alsominimizes resistance to the H₂O diffusing through the water vaporpermeable membrane film deposited on the membrane sheets 34, 36. Themetallic nature of the sheets 34, 36 provides mechanical strength andflexibility for packaging such that the separation module 32 canwithstand a pressure gradient of greater than approximately 60 psi(i.e., approximately 4 times atmospheric pressure).

Separation of water vapor from the other components 30 of the air 14 maycreate a water vapor permeation flux of approximately 1.0 kg/m²/h (e.g.,in a range of approximately 0.5-2.0 kg/m²/h), and a water vapor-to-airselectivity range of approximately 5-200+. As such, the efficiency ofthe dehumidification unit 12 is relatively high compared to otherconventional dehumidification techniques with a relatively low cost ofproduction. As an example, approximately 7-10 m² of membrane area of theinterfaces 20 may be needed to dehumidify 1 ton of air cooling loadunder ambient conditions. In order to handle such an air cooling load,in certain embodiments, 17-20 separation modules 32 having a heighth_(msm) of approximately 450 mm, a length l_(msm) of approximately 450mm, and a width w_(msm) of approximately 5 mm may be used. Theseseparation modules 32 may be assembled side-by-side in thedehumidification unit 12, leaving approximately 2 mm gaps between theseparation modules 32. These gaps define the air channels 16 throughwhich the air 14 flows. The measurements described in this example aremerely exemplary and not intended to be limiting.

FIG. 5 is a psychrometric chart 38 of the temperature and the humidityratio of the moist air 14 flowing through the dehumidification unit 12of FIGS. 1-3 in accordance with an embodiment of the present disclosure.In particular, the x-axis 40 of the psychrometric chart 38 correspondsto the temperature of the air 14 flowing through the air channels 16 ofFIG. 1, the y-axis 42 of the psychrometric chart 38 corresponds to thehumidity ratio of the air 14 flowing through the air channels 16, andthe curve 44 represents the water vapor saturation curve of the air 14flowing through the air channels 16. As illustrated by line 46, becausewater vapor is removed from the air 14 flowing through the air channels16, the humidity ratio of the outlet air 14B (i.e., point 48) from thedehumidification unit 12 of FIGS. 1-3 is lower than the humidity ratioof the inlet air 14A (i.e., point 50) into the dehumidification unit 12of FIGS. 1-3, while the temperature of the outlet air 14B and the inletair 14A are substantially the same.

Returning now to FIG. 1, as described previously, a lower partialpressure of the water vapor 26 (i.e., a partial pressure less than thepartial pressure of water vapor in the air channels 16) is created inthe water vapor channels 18 of the dehumidification unit 12 to furtherfacilitate the passage of H₂O through the interfaces 20 from the airchannels 16 to the water vapor channels 18. In certain embodiments, thewater vapor channels 18 may initially be evacuated using a vacuum pump52. In particular, the vacuum pump 52 may evacuate the water vaporchannels 18 and the water vapor vacuum volume 28, as well as the watervapor outlets 22 and the water vapor manifold 24 of FIG. 2A. However, inother embodiments, a pump separate from the vacuum pump 52 may be usedto evacuate the water vapor channels 18, water vapor vacuum volume 28,water vapor outlets 22, and water vapor manifold 24. As illustrated inFIG. 1, the water vapor 26 removed from the air 14 in thedehumidification unit 12 may be distinguished between the water vapor26A in the water vapor vacuum volume 28 (i.e., the suction side of thevacuum pump 52) and the water vapor 26B expelled from an exhaust side(i.e., an outlet) of the vacuum pump 52 (i.e., the water vapor 26Bdelivered to a condensation unit). In general, the water vapor 26Bexpelled from the vacuum pump 52 will have a slightly higher pressureand a higher temperature than the water vapor 26A in the water vaporvacuum volume 28. The vacuum pump 52 may be a compressor or any othersuitable pressure increasing device capable of maintaining a lowerpressure on the suction side of the vacuum pump 52 than the partialpressure of water vapor in the humid air 14.

For example, the lower partial pressure of water vapor 26A maintained inthe water vapor vacuum volume 28 may be in the range of approximately0.15-0.25 psia, which corresponds to saturation temperatures ofapproximately 45° F. to 60° F., with the water vapor 26A typically be inthe range of approximately 65-75° F. However, in other embodiments, thewater vapor 26A in the water vapor vacuum volume 28 may be maintained ata partial pressure of water vapor in the range of approximately0.01-0.25 psia and a temperature in the range of approximately 55° F. upto the highest ambient air temperature. A specific embodiment may bedesigned to lower the partial pressure in the water vapor vacuum volume28 to the range of 0.01 psia to increase the capacity for removing watervapor from the air 14 to enable an evaporative cooler to process theentire air conditioning load when atmospheric conditions permit thismode of operation.

In certain embodiments, the vacuum pump 52 is a low-pressure pumpconfigured to decrease the pressure of the water vapor 26A in the watervapor vacuum volume 28 to a lower partial pressure than the partialpressure of water vapor on the atmospheric side of the interfaces 20(i.e., the partial pressure of the air 14 in the air channels 16). Onthe exhaust side of the vacuum pump 52, the partial pressure of thewater vapor 26B has been increased just high enough to facilitatecondensation of the water vapor (i.e., in a condensation unit 54).Indeed, the vacuum pump 52 is configured to increase the pressure suchthat the water vapor 26B in the condensation unit 54 is at a pressureproximate to a minimal saturation pressure in the condensation unit 54.

As an example, when in operation, the air 14 may enter the system at apartial pressure of water vapor of 0.32 psia, which corresponds to ahumidity ratio of 0.014 pounds of H₂O per pounds of dry air. The systemmay be set to remove 0.005 pounds of H₂O per pounds of dry air from theair 14. Pressure differentials across the interfaces 20 may be used tocreate a flow of H₂O through the interfaces 20. For example, the partialpressure of water vapor in the water vapor vacuum volume 28 may be setto approximately 0.1 psia. The pressure of the water vapor 26B isincreased by the vacuum pump 52 in a primarily adiabatic process, and asthe pressure of the water vapor 26B increases, the temperature increasesas well (in contrast to the relatively negligible temperaturedifferential across the interfaces 20). As such, if for example thepressure of the water vapor 26B is increased in the vacuum pump 52 by0.3 psi (i.e., to approximately 0.4 psia), the condensation unit 54 isthen capable of condensing the water vapor 26B at a temperature ofapproximately 72-73° F., and the temperature of the water vapor 26B willincrease to a temperature substantially higher than the condensertemperature. The system may continually monitor the pressure andtemperature conditions of both the upstream water vapor 26A and thedownstream water vapor 26B to ensure that the water vapor 26B expelledfrom the vacuum pump 52 has a partial pressure of water vapor just highenough to facilitate condensation in the condensation unit 54. It shouldbe noted that the pressure and temperature values presented in thisscenario are merely exemplary and are not intended to be limiting.

Note that as the pressure difference from the water vapor 26A enteringthe vacuum pump 52 to the water vapor 26B exiting the vacuum pump 52increases, the efficiency of the dehumidification unit 12 decreases. Forexample, in a preferred embodiment, the vacuum pump 52 will be set toadjust the pressure of the water vapor 26B in the condensation unit 54slightly above the saturation pressure at the lowest ambient temperatureof the cooling media (i.e., air or water) used by the condensation unit54 to condense the water vapor 26B. In another embodiment, thetemperature of the water vapor 26B may be used to control the pressurein the condensation unit 54. The temperature of the water vapor 26Bexpelled from the vacuum pump 52 may be substantially warmer than thehumid air 14A (e.g., this temperature could reach 200° F. or abovedepending on a variety of factors). Because the vacuum pump 52 onlyincreases the pressure of the water vapor 26B to a point wherecondensation of the water vapor 26B is facilitated (i.e., approximatelythe saturation pressure), the power requirements of the vacuum pump 52are relatively small, thereby obtaining a high efficiency from thedehumidification unit 12.

Once the water vapor 26B has been slightly pressurized (i.e.,compressed) by the vacuum pump 52, the water vapor 26B is directed intothe condensation unit 54, wherein the water vapor 26B is condensed intoa liquid state. In certain embodiments, the condensation unit 54 mayinclude a condensation coil 56, a pipe/tube condenser, a flat platecondenser, or any other suitable system for causing a temperature belowthe condensation point of the water vapor 26B. The condensation unit 54may either be air cooled or water cooled. For example, in certainembodiments, the condensation unit 54 may be cooled by ambient air orwater from a cooling tower. As such, the costs of operating thecondensation unit 54 may be relatively low, inasmuch as both ambient airand cooling tower water are in relatively limitless supply.

Once the water vapor 26B has been condensed into a liquid state, incertain embodiments, the liquid water from the condensation unit 54 maybe directed into a reservoir 58 for temporary storage of saturated vaporand liquid water. However, in other embodiments, no reservoir 58 may beused. In either case, the liquid water from the condensation unit 54 maybe directed into a liquid pump 60 (i.e., a water transport device),within which the pressure of the liquid water from the condensation unit54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions. As such, the liquid pump 60 may be sized just largeenough to increase the pressure of the liquid water from thecondensation unit 54 to approximately atmospheric pressure. Therefore,the costs of operating the liquid pump 60 may be relatively low. Inaddition, the liquid water from the liquid pump 60 may be at a slightlyelevated temperature due to the increase in the pressure of the liquidwater. As such, in certain embodiments, the heated liquid water may betransported for use as domestic hot water, further increasing theefficiency of the system by recapturing the heat transferred into theliquid water.

Although the interfaces 20 between the air channels 16 and the watervapor channels 18 as described previously generally allow only H₂O topass from the air channels 16 to the water vapor channels 18, in certainembodiments, very minimal amounts (e.g., less than 1% of the oxygen(O₂), nitrogen (N₂), or other noncondensable components) of the othercomponents 30 of the air 14 may be allowed to pass through theinterfaces 20 from the air channels 16 to the water vapor channels 18.Over time, the amount of the other components 30 may build up in thewater vapor channels 18 (as well as in the water vapor vacuum volume 28,the water vapor outlets 22, and the water vapor manifold 24 of FIG. 2A).In general, these other components 30 are noncondensable at thecondenser temperature ranges used in the condensation unit 54. As such,the components 30 may adversely affect the performance of the vacuumpump 52 and all other equipment downstream of the vacuum pump 52 (inparticular, the condensation unit 54).

Accordingly, in certain embodiments, a second vacuum pump may be used toperiodically purge the other components 30 from the water vapor vacuumvolume 28. FIG. 6 is a schematic diagram of the HVAC system 10 and thedehumidification unit 12 of FIG. 1 having a vacuum pump 62 for removingnoncondensable components 30 from the water vapor 26A in the water vaporvacuum volume 28 of the dehumidification unit 12 in accordance with anembodiment of the present disclosure. The vacuum pump 62 may, in certainembodiments, be the same pump used to evacuate the water vapor vacuumvolume 28 (as well as the water vapor channels 18, the water vaporoutlets 22, and the water vapor manifold 24) to create the lower partialpressure of water vapor described previously that facilitates thepassage of the H₂O through the interfaces 20 from the air channels 16 tothe water vapor channels 18. However, in other embodiments, the vacuumpump 62 may be different from the pump used to evacuate the water vaporvacuum volume 28 to create the lower partial pressure of water vapor.

The dehumidification unit 12 described herein may also be controlledbetween various operating states, and modulated based on operatingconditions of the dehumidification unit 12. For example, FIG. 7 is aschematic diagram of the HVAC system 10 and the dehumidification unit 12of FIG. 6 having a control system 64 for controlling various operatingconditions of the HVAC system 10 and the dehumidification unit 12 inaccordance with an embodiment of the present disclosure. The controlsystem 64 may include one or more processors 66, for example, one ormore “general-purpose” microprocessors, one or more special-purposemicroprocessors and/or ASICS (application-specific integrated circuits),or some combination of such processing components. The processors 66 mayuse input/output (I/O) devices 68 to, for example, receive signals fromand issue control signals to the components of the dehumidification unit12 (i.e., the vacuum pumps 52, 62, the condensation unit 54, thereservoir 58, the liquid pump 60, other equipment such as a fan blowingthe inlet air 14A through the dehumidification unit 12, sensorsconfigured to generate signals related to characteristics of the inletand outlet air 14A, 14B, and so forth). The processors 66 may take thesesignals as inputs and calculate how to control the functionality ofthese components of the dehumidification unit 12 to most efficientlyremove the water vapor 26 from the air 14 flowing through thedehumidification unit 12. The control system 64 may also include anontransitory computer-readable medium (i.e., a memory 70) which, forexample, may store instructions or data to be processed by the one ormore processors 66 of the control system 64.

For example, the control system 64 may be configured to control the rateof removal of the noncondensable components 30 of the water vapor 26Afrom the water vapor vacuum volume 28 of the dehumidification unit 12 byturning the vacuum pump 62 on or off, or by modulating the rate at whichthe vacuum pump 62 removes the noncondensable components 30 of the watervapor 26A. More specifically, in certain embodiments, the control system64 may receive signals from a sensor in the water vapor vacuum volume 28that detects when too many noncondensable components 30 are present inthe water vapor 26A contained in the water vapor vacuum volume 28. Thisprocess of noncondensable component removal will operate in a cyclicalmanner. In “normal” operation of removing the water vapor 26 from theair 14, the vacuum pump 62 will not be in operation. As thenoncondensable components 30 build up in the water vapor vacuum volume28, the internal pressure in the water vapor vacuum volume 28 willeventually reach a setpoint. At this point in time, the vacuum pump 62will turn on and remove all components (i.e., both the noncondensablecomponents 30 as well as H₂O, including the water vapor) until theinternal pressure in the water vapor vacuum volume 28 reaches anothersetpoint (e.g., lower than the starting vacuum pressure). Then, thevacuum pump 62 shuts off and the dehumidification unit 12 returns to thenormal operational mode. Setpoints may either be preset or dynamicallydetermined. A preferred method will be to have the vacuum pump 62 onlyoperating in the purge mode intermittently.

Another example of the type of control that may be accomplished by thecontrol system 64 is modulating the lower partial pressure of the watervapor 26A in the water vapor vacuum volume 28 (as well as the watervapor channels 18, the water vapor outlets 22, and the water vapormanifold 24) to modify the water vapor removal capacity and efficiencyratio of the dehumidification unit 12. For example, the control system64 may receive signals from pressure sensors in the water vapor vacuumvolume 28, the water vapor channels 18, the water vapor outlets 22,and/or the water vapor manifold 24, as well as signals generated bysensors relating to characteristics (e.g., temperature, pressure, flowrate, relative humidity, and so forth) of the inlet and outlet air 14A,14B, among other things. The control system 64 may use this informationto determine how to modulate the lower partial pressure of the watervapor 26A (e.g., with respect to the partial pressure of water vapor inthe air 14 flowing through the air channels 16) to increase or decreasethe rate of removal of water vapor 26 from the air channels 16 to thewater vapor channels 18 through the interfaces 20.

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volume 28 maybe reduced and, conversely, if less water vapor removal is desired, thelower partial pressure of the water vapor 26A in the water vapor vacuumvolume 28 may be increased. Furthermore, in certain embodiments, theamount of dehumidification (i.e., water vapor removal) may be cycled toimprove the efficiency of the dehumidification unit 12. Morespecifically, under certain operating conditions, the dehumidificationunit 12 may function more efficiently at higher rates of water vaporremoval. As such, in certain embodiments, the dehumidification unit 12may be cycled to remove a maximum amount of water vapor from the air 14for a while, then to remove relatively no water vapor from the air 14for a while, then to remove a maximum amount of water vapor from the air14 for a while, and so forth. In other words, the dehumidification unit12 may be operated at full water vapor removal capacity for periods oftime alternating with other periods of time where no water vapor isremoved. In addition, the control system 64 may be configured to controlstart-up and shutdown sequencing of the dehumidification unit 12.

The dehumidification unit 12 may be designed and operated in manyvarious modes, and at varying operating conditions. In general, thedehumidification unit 12 will be operated with the water vapor vacuumvolume 28 (as well as the water vapor channels 18, the water vaporoutlets 22, and the water vapor manifold 24) at a water vapor partialpressure below the water vapor partial pressure of the air 14 flowingthrough the air channels 16. In certain embodiments, thedehumidification unit 12 may be optimized for dedicated outside airsystem (DOAS) use, wherein the air 14 may have a temperature in therange of approximately 55-100° F., and a relative humidity in the rangeof approximately 55-100%. In other embodiments, the dehumidificationunit 12 may be optimized for residential use for recirculated air havinga temperature in the range of approximately 70-85° F., and a relativehumidity in the range of approximately 55-65%. Similarly, in certainembodiments, the dehumidification unit 12 may be optimized fordehumidifying outside air in commercial building recirculated airsystems, which dehumidifies the inlet air 14A having a temperature inthe range of approximately 55-110° F., and a relative humidity in therange of approximately 55-100%. The outlet air 14B has less humidity andabout the same temperature as the inlet air 14A, unless cooling isperformed on the outlet air 14B.

The dehumidification unit 12 described herein requires less operatingpower than conventional dehumidification systems because of therelatively low pressures that are required to dehumidify the air 14A.This is due at least in part to the ability of the interfaces 20 (i.e.,water vapor permeable membranes) to remove the water vapor 26 from theair 14 efficiently without requiring excessive pressures to force thewater vapor 26 through the interfaces 20. For example, in oneembodiment, the minimal power needed to operate the dehumidificationunit 12 includes only the fan power required to move the air 14 throughthe dehumidification unit 12, the compressive power of the vacuum pump52 to compress the water vapor 26 to approximately the saturationpressure (for example, to approximately 1.0 psia, or to a saturationpressure that corresponds to a given condensation temperature, forexample, approximately 100° F.), the pumping and/or fan power of thecondensation unit 54 (e.g., depending on whether cooling tower water orambient air is used as the cooling medium), the pumping power of theliquid pump 60 to reject the liquid water from the condensation unit 54at ambient conditions, and the power of the vacuum pump 62 to purgenoncondensable components 30 that leak into the water vapor vacuumvolume 28 of the dehumidification unit 12. As such, the only relativelymajor power component required to operate the dehumidification unit 12is the compressive power of the vacuum pump 52 to compress the watervapor 26 to approximately the saturation pressure (for example, only toapproximately 1.0 psia, or to a saturation pressure that corresponds toa given condensation temperature, for example, approximately 100° F.).As mentioned previously, this power is relatively low and, therefore,operating the dehumidification unit 12 is relatively inexpensive asopposed to conventional refrigeration compression dehumidificationsystems. Moreover, calculations for an embodiment indicate that thedehumidification unit 12 has a coefficient of performance (COP) at leasttwice as high (or even up to five times as high, depending on operatingconditions) as these conventional dehumidification systems. In addition,the dehumidification unit 12 enables the dehumidification of air withoutreducing the temperature of the air below the temperature at which theair is needed, as is often done in conventional dehumidificationsystems.

While the present disclosure may be susceptible to various modificationsand alternative forms, specific embodiments have been shown by way ofexample in the drawings and tables and have been described in detailherein. However, it should be understood that the embodiments are notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosure as defined by thefollowing appended claims. Further, although individual embodiments arediscussed herein, the disclosure is intended to cover all combinationsof these embodiments.

1. A dehumidification system for removing water vapor from an airstream,comprising: a first and second channel separated by a membrane, whereinthe membrane is configured to facilitate removal of water vapor from anairstream flowing through the first channel by facilitating passage ofH₂O from the water vapor to the second channel through permeable volumesof the membrane while substantially blocking all other components of theairstream from passing through the membrane; a pressure increasingdevice configured to create a lower partial pressure of water vaporwithin the second channel than in the first channel, such that the H₂Omoves through the membrane to the second channel, wherein the pressureincreasing device is also configured to increase the pressure of watervapor at an outlet of the pressure increasing device to a partialpressure of water vapor in a range suitable for subsequent condensinginto liquid water; a condensation device configured to receive the watervapor from the pressure increasing device and condense the water vaporinto liquid water; and a water transport device configured to transportthe liquid water from the condensation device.
 2. The system of claim 1,comprising a controller configured to control start-up, shutdown, andoperation of the system.
 3. The system of claim 1, comprising acontroller configured to optimize the operation of the system.
 4. Thesystem of claim 1, comprising a vacuum pump that removes noncondensablecomponents from water vapor in the second channel.
 5. The system ofclaim 4, comprising a controller configured to control and optimize therate of removal of the noncondensable components from water vapor in thesecond channel by the vacuum pump.
 6. A system, comprising: adehumidification system for removing H₂O vapor from an airstream,comprising: an air channel configured to receive an inlet airstream anddischarge an outlet airstream; an H₂O permeable material adjacent to theair channel, wherein the H₂O permeable material is configured toselectively enable H₂O from H₂O vapor in the inlet airstream to passthrough the H₂O permeable material to a suction side of the H₂Opermeable material and substantially block other components in the inletairstream from passing through the H₂O permeable material to the suctionside of the H₂O permeable material; a pressure increasing deviceconfigured to create a lower partial pressure of H₂O vapor on thesuction side of the H₂O permeable material than the partial pressure ofthe H₂O vapor in the inlet airstream to drive passage of the H₂O fromthe H₂O vapor in the inlet airstream through the H₂O permeable material,and to increase the pressure at an outlet of the pressure increasingdevice to a partial pressure of H₂O vapor suitable for condensing H₂Ovapor into liquid H₂O; and a condensation device configured to receivethe H₂O vapor from the outlet of the pressure increasing device, and tocondense the H₂O vapor into liquid H₂O.
 7. The system of claim 6,comprising a liquid pump configured to transport the liquid H₂O from thecondensation device.
 8. The system of claim 6, wherein the pressureincreasing device comprises a vacuum pump.
 9. The system of claim 6,wherein the H₂O permeable material comprises an H₂O permeable membrane.10. The system of claim 6, wherein the H₂O permeable material compriseszeolite.
 11. The system of claim 6, wherein the condensation devicecomprises a condensation coil that condenses the H₂O vapor into liquidH₂O.
 12. The system of claim 6, wherein the dehumidification systemcomprises a vacuum pump that removes noncondensable components from H₂Ovapor on the suction side of the H₂O permeable material.
 13. The systemof claim 12, comprising a controller configured to periodically purgethe suction side of the H₂O permeable material.
 14. The system of claim6, comprising a controller configured to modulate the lower partialpressure of H₂O vapor on the suction side of the H₂O permeable materialto modify the H₂O removal capacity and efficiency of thedehumidification system.
 15. A method, comprising: using a pressuredifferential across an H₂O permeable material to provide a force to moveH₂O through the H₂O permeable material into an H₂O vapor channel;receiving H₂O vapor from the H₂O permeable material into the H₂O vaporchannel; receiving the H₂O vapor from the H₂O vapor channel into apressure increasing device and expelling the H₂O vapor from the pressureincreasing device at a slightly increased partial pressure of H₂O vapor;receiving the H₂O vapor from the pressure increasing device into acondensation device and condensing the H₂O vapor into liquid H₂O; andtransporting the liquid H₂O from the condensation device to ambientconditions.
 16. The method of claim 15, comprising receiving anairstream including the H₂O into an air inlet channel, and using thepressure differential across the H₂O permeable material to provide theforce to move H₂O from the airstream through the H₂O permeable materialinto the H₂O vapor channel.
 17. The method of claim 15, comprisingsubstantially blocking passage of other components of the airstreamthrough the H₂O permeable material.
 18. The method of claim 17, whereinthe H₂O permeable material comprises an H₂O permeable membrane.
 19. Themethod of claim 17, wherein the H₂O permeable material compriseszeolite.
 20. The method of claim 15, wherein the H₂O vapor channel has apartial pressure of H₂O vapor in a range of approximately 0.1-0.25 psia.